|Mammalia (Mammals): Chiroptera, Vespertillionidae
Townsend’s Big-Eared Bat (Corynorhinus townsendii)
Potential Occurrence: Unlikely to Occur
Photo: New Mexico Energy 2008
State: Species of Special Concern
The Townsend’s big-eared bat (Corynorhinus townsendii) is a member of the taxonomic Order Chiroptera and Family Vespertilionidae. It is a medium-sized (8-14 g) bat with rabbit-like ears, a small indistinct face and overall brownish coloration. This species is related in appearance to only one other bat with very large ears, the pallid bat (Antrozous pallidus), which is larger overall, light-colored, with large eyes and a distinct muzzle. (From Fricke 2009)
Townsend's big-eared bat is found throughout California, but the details of its distribution are not well known. This species is found in all but subalpine and alpine habitats, and may be found at any season throughout its range. Once considered common, Townsend's big-eared bat now is considered uncommon in California. It is most abundant in mesic habitats. (From Harris 2000)
Life History & Threats:
The life history of the Townsend’s big-eared bat centers on reproduction and meeting the energetic demands of a small insectivorous mammal. Its annual cycle includes an approximate 7 to 8 month period of peak activity in spring and summer when insects are most available and reproduction occurs. Pregnant females gather in maternity colonies which range in size from a few to several hundred individuals. Males usually roost elsewhere, singly or in small numbers. Maternity colonies form between March and June (based on local climatic factors), with a single pup born between May and July (Pearson et al. 1952). Maternity colonies cluster tightly together to share body heat and the appearance of the cluster is characteristic. Although roost site fidelity is variable in areas with many potential roost sites, it is quite high in California where roosting habitat is scarce (Sherwin et al. 2003). The Townsend’s big-eared bat uses daily and seasonal periods of hibernation to conserve energy when it is inactive. In winter months when insect prey is less available this species extends hibernation over weeks or months and it may migrate locally to suitable hibernation sites. (From Fricke 2009)
Townsend’s big-eared bats are highly sensitive to roost disturbance. Activities that can result in significant disturbance or loss of habitat include mine reclamation, renewed mining, water impoundments, recreational caving, loss of building roosts, and bridge replacement (Kunz and Martin 1982, Pierson et al. 1999). Pesticide contamination may also threaten this species in agricultural areas (Geluso et al. 1976). (From Contra Costa County HCP/NCCP 2006)
Habitat & Habitat Associations:
Generally, Townsend’s big-eared bats are found in the dry uplands throughout the West, but they also occur in mesic coniferous and deciduous forest habitats along the Pacific coast (Kunz and Martin 1982). (From Gruver 2006)
Townsend’s big-eared bat has been noted foraging in a wide variety of habitats (Pierson et al. 1999) throughout its western range, and this may reflect the need to roost where structures are available as opposed to within a particular vegetative zone. Given its wing morphology, which permits slow maneuverable flight and the ability to hover and glean insects from vegetation (Norberg and Rayner 1987), Corynorhinus townsendii is expected to forage primarily in and near vegetation, and to engage in little if any of the open-air hawking that is characteristic of swift-flying species such as hoary bats (Lasiurus cinereus). Thus, suitable foraging habitat for C. townsendii will likely be a heterogeneous mosaic of forested and edge habitats, including riparian zones, which are also used for commuting and drinking (e.g., Fellers and Pierson 2002). In California, both males and females foraged along the edges of riparian vegetation dominated by Douglas-fir, California bay, and willow species, but they also avoided open grasslands both when traveling and foraging (Fellers and Pierson 2002). (From Gruver 2006)
Areas with substantial beaver activity enhance the quality of foraging habitat by increasing ecosystem productivity (Naiman et al. 1986), providing gaps in the forest canopy, providing small, quiet ponds for drinking, and causing an increase in insect activity. (From Gruver 2006)
Roosts, Hibernacula, and Nurseries:
Townsend’s big-eared bat is unequivocally associated with areas containing caves and cave-analogs for roosting habitat. Beyond the constraint for cavernous roosts, habitat associations become less well defined. Townsend’s big-eared bat requires spacious cavern-like structures for roosting (Pierson et al. 1999) during all stages of its life cycle. Typically, they use caves and mines, but Corynorhinus townsendii have been noted roosting in large hollows of redwood trees (Fellers and Pierson 2002), in attics and abandoned buildings (Dalquest 1947, Fellers and Pierson 2002), in lava tubes (Handley 1959, Hinman and Snow 2004), and under bridges (Keeley 1998, Adam and Hayes 2000, Fellers and Pierson 2002). (From Gruver 2006)
Conceptual Basis for GIS Model Development:
Habitat for Townsend’s Big-Eared Bat occurs throughout the Study Area. To more specifically define potential habitat use, we mapped:
Best Foraging Habitat:
edges of woodland and forests (i.e., boundaries of cismontane, broadleaf upland, coniferous, and riparian woodland and forest)
ponds and perennial or seasonal watercourses
Best Roosting, Hibernacula and Nursery Habitat:
coniferous forest with > 61 cm in DBH, the largest size class documented in the Study Area. Large, coniferous trees were mapped to indicate the most likely locations for large redwood trees which may contain the cavernous cavities used by this species.
Data on caves locations are not available.
Potential Occurrence in the Galbreath Wildlands Preserve:
Habitat: Townsend’s Big-Eared Bats are habitat generalists found in areas containing cavernous roost sites (caves, redwood cavities, and abandoned buildings). Without focused surveys to locate potential roosting habitat, habitat quality for this species is difficult to determine:
Caves may occur on the preserve but are likely rare. Rocky outcrops and ridgelines do occur but are rarely large enough to accommodate the development of a substantial cavern.
Redwood cavities may also occur but are likely limited. Logging in the Preserve was discontinued in 2000, but has a long history of timber harvest. Some old growth redwoods still occur in isolated locations.
Abandoned buildings on the Preserve are limited to two sheep barns which are currently not known to support roosting bats.
We conclude that roosting habitat required by this species may be good quality if present, but is likely very limited in abundance (Figure 103).
Documented Occurrences in the Preserve: This species has not been documented in the Preserve. To our knowledge, no surveys have been conducted.
Nearest Occurrence to Preserve: This species has not been reported to occur in USGS quads adjacent to the Preserve, but is widespread throughout California.
Summary: Townsend’s Big-Eared Bats are “Unlikely to Occur” in the Study Area due to possible limitations on the availability of roosting habitat. Further surveys are needed to assess this species likelihood of occurrence.
East Contra Costa County HCP/NCCP. 2006 October. Species Account – Townsend’s Western
Big-Eared Bat (Corynorhinus townsendii townsendii).
06_profile.pdf> 2010 June 18.
Giusti, GA. 2007. Structural Characteristics of an Old-Growth Coast Redwood Stand in Mendocino County, California. Proceedings of the redwood region forest science symposium: What does the Future Hold? Gen. Tech. Rep. PSW-GTR-194. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; p. 161-168
Gruver, J.C. and D.A. Keinath. 2006 October 25. Townsend’s Big-eared Bat (Corynorhinus
townsendii): a technical conservation assessment. USDA Forest Service, Rocky
Mountain Region. <http://www.fs.fed.us/r2/projects/scp/assessments/ townsendsbigearedbat.pdf> 2010 June 18
Harris J. 2000. Townsend’s Big-Eared Bat. California Wildlife Habitat Relationships System.
2010 June 18.
Johnson H, Fricke W, and D Johnston. 2009 April 20. Yolo Natural Heritage Program-Draft
Species Accounts-Townsends Big-Eared Bat. Technology Associates.
big-eared-bat.pdf> 2010 June 24.
New Mexico Energy, Minerals and Natural Resources Department. 2008 June 25. Townsend’s
Big-Eared Bat Photo. Bats in New Mexico – Townsend’s Big-Eared Bat.
emnrd.state.nm.us/mmd/aml/Bat%20list/AMLtownsendsbigearedbat.htm> 2010 June 18.
Species Account Description: Emily Harvey